Conventionally, the fabrication of wafer-level chip scale packages, WLCSP, is to form a plurality of bumps on a semiconductor wafer firstly, then the wafer is singulated to form a plurality of individual WLCSP including a chip, whereas, bumps are used as outer electrical terminals of the WLCSP (chip) to an exterior printed circuit board, PCB. However, during the IC operation, the chip will generate heat which will cause extra thermal stress on the bumps due to mismatching of thermal expansion coefficients between the chip and PCB. Thus, bumps will easily break or even fail. As revealed in U.S. Pat. No. 6,187,615, “chip scale packages and methods for manufacturing the chip scale packages at wafer level”, a reinforcing layer is formed around the bumps to absorb the extra thermal stress on the bumps. The reinforcing layer is made of low-viscosity polymers which can be easily coated between the bumps before curing. After curing, the reinforcing layer will be able to protect the bumps from bump failure. However, during the coating process, bump surfaces for electrical connection can be coated with the reinforcing layer easily due to the characteristics of low-viscosity polymers and cause bad solder joint even electrical open between WLCSP and PCB after assembly.